The present invention pertains to the art of making golf balls, and, more particularly, to a new die configuration for use in reaction injection molding of golf ball layers and covers.
Golf balls are typically made by molding a core of elastomeric or polymeric material into a spheroid shape. A cover is then molded around the core. Sometimes, before the cover is molded about the core, an intermediate layer is molded about the core and the cover is then molded around the intermediate layer. The molding processes used for the cover and the intermediate layer are similar and usually involve either compression molding or injection molding.
In compression molding, the golf ball core is inserted into a central area of a two piece die and pre-sized sections of cover material are placed in each half of the die, which then clamps shut. The application of heat and pressure molds the cover material about the core.
Blends of polymeric materials have been used for modern golf ball covers because certain grades and combinations have offered certain levels of hardness, to resist damage when the ball is hit with a club, and elasticity, to allow responsiveness to the hit. Some of these materials facilitate processing by compression molding, yet disadvantages have arisen. These disadvantages include the presence of seams in the cover, which occur where the pre-sized sections of cover material were joined, and high process cycle times which are required to heat the cover material and complete the molding process.
Injection molding of golf ball covers arose as a processing technique to overcome some of the disadvantages of compression molding. The process involves inserting a golf ball core into a die, closing the die and forcing a heated, viscous polymeric material into the die. The material is then cooled and the golf ball is removed from the die. Injection molding is well-suited for thermoplastic materials, but has limited application to some thermosetting polymers. However, certain types of these thermosetting polymers often exhibit the hardness and elasticity desired for a golf ball cover. Some of the most promising thermosetting materials are reactive, requiring two or more components to be mixed and rapidly transferred into a die before a polymerization reaction is complete. As a result, traditional injection molding techniques do not provide proper processing when applied to these materials.
Reaction injection molding is a processing technique used specifically for certain reactive thermosetting plastics. As mentioned above, by xe2x80x9creactivexe2x80x9d it is meant that the polymer is formed from two or more components which react. Generally, the components, prior to reacting, exhibit relatively low viscosities. The low viscosities of the components allow the use of lower temperatures and pressures than those utilized in traditional injection molding. In reaction injection molding, the two or more components are combined and react to produce the final polymerized material. Mixing of these separate components is critical, a distinct difference from traditional injection molding.
The process of reaction injection molding a golf ball cover involves placing a golf ball core into a die, closing the die, injecting the reactive components into a mixing chamber where they combine, and transferring the combined material into the die. The mixing begins the polymerization reaction which is typically completed upon cooling of the cover material.
The present invention provides a new mold or die configuration and a new method of processing for reaction injection molding a golf ball cover or inner layer which promotes increased mixing of constituent materials, resulting in enhanced properties and the ability to explore the use of materials new to the golf ball art.
In accordance with one embodiment of the present invention, an apparatus for making a golf ball is provided. The apparatus is a mold for making a golf ball which includes a body and a cavity defined within the body for retaining a golf ball core. The mold provides a molding cavity, at least one material flow inlet, and at least one material flow channel providing fluid communication between the molding cavity and the material flow inlet. The mold additionally provides at least a portion of the material flow channel having a plurality of bends and at least one branching intersection that promotes turbulence in a liquid molding material flowing therethrough.
In accordance with another embodiment of the present invention, a method of making a golf ball is provided. The method includes providing a molding assembly including a mold defining a molding cavity adapted to receive a golf ball core and a material flow channel providing fluid communication between the molding cavity and a source of flowable molding material. The material flow channel has at least one turbulence-promoting fan gate. The method further includes obtaining a golf ball core, positioning the core within the molding cavity, and introducing an effective amount of the flowable molding material through the material flow channel and into the molding cavity thereby causing the flowable molding material to pass through the turbulence-promoting fan gate and forming a layer of the molding material about the core.
In accordance with another embodiment of the present invention, a golf ball is provided. The golf ball includes a core and at least one layer formed from a reaction injected molded material surrounding the core. The layer preferably has a thickness of about 0.015 inches to 0.050 inches.
One advantage of the present invention is that the constituent materials are mixed thoroughly, thereby providing a more consistent intermediate and/or cover layer, resulting in better golf ball performance characteristics.
Another advantage of the present invention is that the use of new, lower viscosity materials may be explored, resulting in enhanced golf ball properties and performance.
Yet another advantage of the present invention is that increased mixing of lower viscosity materials allows the intermediate layer or cover to be thinner, resulting in increased ball performance.
Still another advantage of the present invention is that a unique venting configuration of the mold reduces the porosity of the material being processed, creating a ball cover or other layer that is substantially free from voids.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.